20 



VETERINARY STUDIES 



The navicular bone is also a sesamoid bone; i.e., it is formed 

 in tendon. It is a short bone in structure, but rather long and 

 slender in shape, and placed crosswise just back of the articu- 

 lation between the second and third phalanges. Its inferior 

 surface is smooth except for a slight ridge in the center. The 

 tendon of the deep flexor muscle passes over this surface on its 

 way to its insertion on the bottom of the third phalanx. The 

 ends of the navicular bone unite on each side with the wings of 

 the third phalanx by tough fibrous tissue. 



Fig. 14. — The Hoof. 



The Wall. A, Toe; B, quarter; C, heel. 



Ground Surface, a-a, toe; a-b, quarter; b-d, heel; c, bar; /, /, f, sole; 

 g, white line; h, frog; I, cleft of the frog. 



Horny hoof. — This is to be regarded as an appendage of the 

 skin. It covers all of the third phalanx and part of the second. 

 It is divided for study into wall, sole, and frog. 



The wall is that part which may be seen when looking at the 

 hoof in front and at the sides when the foot is on the ground. 

 It is composed of horny, tubular fibers, which grow from the 

 coronary band. Between these tubular fibers is a material which 

 holds them together. The wall is divided into toe, quarters, and 

 heels. At the top is a groove into which the coronary band fits, 

 the crown of the hoof. The wall unites below with the sole. 

 The smooth shining layer which should cover the surface 

 of the wall is periople. The duty of this layer is to prevent 

 undue evaporation from the hoof. Beneath the periople is the 

 horny wall which gives shape to the foot and protects the soft 

 parts within. Inside this hard layer come the laminae ; these 

 are thin leaves of horny material which dovetail in with the 

 sensitive laminae. 



